This invention relates generally to electronically controlled ignition systems for internal combustion engines, and in particular to an ignition control system which is adapted to control the spark timing of the engine over a variety of engine running conditions.
Internal combustion engines have conventionally embodied mechanically operated spark advance mechanisms for controlling the spark advance in relation to throttle valve opening. Normally, the arrangement embodies a movably supported sensing device that is positioned in proximity to the engine crankcase and which generates a signal in response to the crankshaft rotation for intiating spark timing. Either the sensing device or some other associated component is rotated relative to a fixed component of the engine so as to change the spark timing. Normally, the spark timing is such that the spark is advanced to a predetermined angle at a given throttle valve opening and then is held at that angle. However, actual spark advance timing requirements are dependent upon other conditions than throttle openings and the previously proposed mechanically operated devies have not been able to produce the desired spark timing under all running conditions.
Electronically controlled ignition systems have also been proposed for controlling the spark timing electronically. Although such devices generally afford greater latitude in the timing control and the number of conditions which they are responsive to, the previously proposed systems have not been fully effective under all running conditions. One prior system which is principally directed to electronically advancing the spark timing is disclosed in the assignee's copending U.S. patent application Ser. No. 525,316, entitled "Electronically Controlled Ignition Angle Advancing Device For Internal Combustion Engines", filed on Aug. 22, 1983, to Gohara, et al. This patent application is hereby incorporated by reference.
It is therefore a principal object of the present invention to provide an improved ignition control system for an internal combustion engine and an improved method for electronically controlling the spark timing over a wide range of engine operating conditions.
It is another object of the present invention to provide an ignition control system which not only can advance and retard the spark timing, but is also capable of causing controlled engine misfires under the appropriate engine operating conditions.
It is a further object of the present invention to provide an ignition control system in which the spark timing is selectively a function of the engine temperature, the engine speed and the air flow to this engine induction system.
It is an additional object of the present invention to provide an ignition control system which is selectively responsive to abnormal combustion running conditions so as to assure smooth engine operation.
It is yet another object of the present invention to provide an ignition control device which is capable of suppressing an overheat running condition of the engine by automatically and gradually reducing the speed of the engine.